The earliest evidence of Native American settlement in the Miami region came from about 12,000 years ago.[4] The first inhabitants settled on the banks of the Miami River, with the main villages on the northern banks.

The inhabitants at the time of first European contact were the Tequesta people, who controlled much of southeastern Florida, including what is now Miami-Dade County, Broward County, and the southern part of Palm Beach County. The Tequesta Indians fished, hunted, and gathered the fruit and roots of plants for food, but did not practice any form of agriculture. They buried the small bones of the deceased with the rest of the body, and put the larger bones in a box for the village people to see. The Tequesta are credited with making the Miami Circle.[5]

Juan Ponce de León was the first European to visit the area in 1513 by sailing into Biscayne Bay. His journal records that he reached Chequescha, a varianth of Tequesta, which was Miami's first recorded name.[6] It is unknown whether he came ashore or made contact with the natives. Pedro Menéndez de Avilés and his men made the first recorded landing when they visited the Tequesta settlement in 1566 while looking for Avilés' missing son, shipwrecked a year earlier.[7] Spanish soldiers led by Father Francisco Villarreal built a Jesuit mission at the mouth of the Miami River a year later but it was short-lived. After the Spaniards left, the Tequesta Indians were left to fend themselves from European-introduced diseases like smallpox. By 1711, the Tequesta sent a couple of local chiefs to Havana, Cuba, to ask if they could migrate there. The Cubans sent two ships to help them, but Spanish illnesses struck and most of the Indians died.[8]

The first permanent European settlers arrived in the early 19th century. People came from the Bahamas to South Florida and the Keys to hunt for treasure from the ships that ran aground on the treacherous Great Florida Reef. Some accepted Spanish land offers along the Miami River. At about the same time, the Seminole Indians arrived, along with a group of runaway slaves. The area was affected by the Second Seminole War, during which Major William S. Harney led several raids against the Indians. Most non-Indian residents were soldiers stationed at Fort Dallas. It was the most devastating Indian war in American history, causing almost a total loss of population in the Miami.

After the Second Seminole War ended in 1842, William English, re-established a plantation started by his uncle on the Miami River. He charted the “Village of Miami” on the south bank of the Miami River and sold several plots of land. In 1844, Miami became the county seat, and six years later a census reported that there were ninety-six residents living in the area.[9] The Third Seminole War was not as destructive as the second one. Even so, it slowed down the settlement of southeast Florida. At the end of the war, a few of the soldiers stayed.

Dade County was created on January 18, 1836, under the Territorial Act of the United States. The county was named after Major Francis L. Dade, a soldier killed in 1835 in the Second Seminole War, at what has since been named the Dade Battlefield.[10] At the time of its creation, Dade County included the land that now contains Palm Beach and Broward counties, together with the Florida Keys from Bahia Honda Key north and the land of present day Miami-Dade County. The county seat was originally at Indian Key in the Florida Keys; then in 1844, the County seat was moved to Miami. The Florida Keys from Key Largo to Bahia Honda were returned to Monroe County in 1866. In 1888 the county seat was moved to Juno, near present-day Juno Beach, Florida, returning to Miami in 1899. In 1909, Palm Beach County was formed from the northern portion of what was then Dade County, and then in 1915, Palm Beach County and Dade County contributed nearly equal portions of land to create what is now Broward County. There have been no significant boundary changes to the county since 1915.[11][12][13]

The third-costliest natural disaster to occur in the United States was Hurricane Andrew, which hit Miami early Monday morning on August 24, 1992. It struck the southern part of the county from due east, south of Miami and very near Homestead, Kendall, and Cutler Ridge (now the Town of Cutler Bay). Damages numbered over US$25 billion in the county alone, and recovery has taken years in these areas where the destruction was greatest. This was the costliest natural disaster in US history until Hurricane Katrina struck the Gulf region in 2005.

On November 13, 1997, voters changed the name of the county from Dade to Miami-Dade to acknowledge the international name recognition of Miami.[14] Voters were acting pursuant to home rule powers granted to Dade County, including the ability to change the name of the county without the consent of the Florida Legislature.[15] The change in name also addressed a source of public dissatisfaction with the name "Dade" which was chosen to honor of Francis L. Dade, who had been killed in the Dade Massacre in the 1830s. The Dade Massacre did not occur in South Florida, but rather, in the West Central part of the state, in present day Sumter County, Florida, near Bushnell. There is also a Dade City, Florida, which is closer to the site of the massacre.

According to the U.S. Census Bureau, the county has a total area of 2,431 square miles (6,300 km2), of which 1,898 square miles (4,920 km2) is land and 533 square miles (1,380 km2) (21.9%) is water.[16] It is the third-largest county in Florida by land area and second-largest by total area. Most of the water is in the Biscayne Bay, with another significant portion in the adjacent waters of the Atlantic Ocean.

Miami-Dade County is only about 6 feet (1.8 m) above sea level. It is rather new geologically and located at the eastern edge of the Florida Platform, a carbonate plateau created millions of years ago. Eastern Dade is composed of Oolitelimestone while western Dade is composed mostly of Bryozoa.[17] Miami-Dade is among the last areas of Florida to be created and populated with fauna and flora, mostly in the Pleistocene.

The bay is divided from the Atlantic Ocean by the many barrier isles along the coast, one of which is where well-known Miami Beach is located, home to South Beach and the Art Deco district. The Florida Keys, which are also barrier islands are only accessible through Miami-Dade County, but which are otherwise part of neighboring Monroe County. Miami is situated seventy miles from West Palm Beach, and thirty miles from Fort Lauderdale.

There were 776,774 households out of which 33.8% had children under the age of 18 living with them, 47.7% were married couples living together, 17.2% had a female householder with no husband present, and 29.4% were non-families. 23.3% of all households were made up of individuals and 8.6% had someone living alone who was 65 years of age or older. The average household size was 2.84 and the average family size was 3.35.

The age distribution is 24.8% under the age of 18, 9.1% from 18 to 24, 31.0% from 25 to 44, 21.7% from 45 to 64, and 13.3% who were 65 years of age or older. The median age was 36 years. For every 100 females there were 93.5 males. For every 100 females age 18 and over, there were 90.2 males.

The median income for a household in the county was $35,966, and the median income for a family was $40,260. Males had a median income of $30,120 versus $24,686 for females. The per capita income for the county was $18,497. About 14.5% of families and 18.0% of the population were below the poverty line, including 22.9% of those under age 18 and 18.9% of those age 65 or over.

Hewlett Packard's main Latin America offices are located on the ninth floor of the Waterford Building in unincorporated Miami-Dade County.[42]

AstraZeneca has its Latin American headquarters in an unincorporated area.[43]Gate Group has its Latin American headquarters in an unincorporated area.[44]Unicomer Group has its United States offices in an unincorporated area.[45]TAME has its United States offices in an unincorporated area.[46]

After Frank Borman became president of Eastern Airlines in 1975, he moved Eastern's headquarters from Rockefeller Center in Midtown Manhattan, New York City to an unincorporated area in Miami-Dade County[51][52] Around 1991 the Miami-Dade County lost a few corporations, including Eastern Airlines, which folded in 1991.[53]

At one time the cruise line ResidenSea had its headquarters in an unincorporated area in the county.[54]

Miami-Dade County has operated under a unique metropolitan system of government, a "two-tier federation," since 1957. This was made possible when Florida voters approved a constitutional amendment in 1956 that allowed the people of Dade County (as it was known then) to enact a home rulecharter. Prior to this year, home rule did not exist in Florida, and all counties were limited to the same set of powers by the Florida Constitution and state law. Mattie Belle Davis, the first woman from Florida elected to the American Bar Foundation and the second woman to be elected in the US, was the first woman judge of Metropolitan Court of Dade County, Florida.

Unlike a consolidated city-county, where the city and county governments merge into a single entity, these two entities remain separate. Instead there are two "tiers", or levels, of government: city and county. There are 35 municipalities in the county, the City of Miami being the largest.

District

Commissioner

1st

Barbara J. Jordan

2nd

Jean Monestime, Chairman

3rd

Audrey Edmonson

4th

Sally A. Heyman

5th

Bruno A. Barreiro

6th

Rebeca Sosa

7th

Xavier L. Suarez

8th

Danielle Levine Cava

9th

Dennis C. Moss

10th

Javier D. Souto

11th

Juan C. Zapata

12th

José "Pepe" Diaz

13th

Esteban Bovo, Jr.

Cities are the "lower tier" of local government, providing police and fire protection, zoning and code enforcement, and other typical city services within their jurisdiction. These services are paid for by city taxes. The County is the "upper tier", and it provides services of a metropolitan nature, such as emergency management, airport and seaport operations, public housing and health care services, transportation, environmental services, solid waste disposal etc. These are funded by county taxes, which are assessed on all incorporated and unincorporated areas.

Of the county's 2.2 million total residents (as of 2000), approximately 52% live in unincorporated areas, the majority of which are heavily urbanized. These residents are part of the Unincorporated Municipal Services Area (UMSA). For these residents, the County fills the role of both lower- and upper-tier government, the County Commission acting as their lower-tier municipal representative body. Residents within UMSA pay a UMSA tax, equivalent to a city tax, which is used to provide County residents with equivalent city services (police, fire, zoning, water and sewer, etc.). Residents of incorporated areas do not pay UMSA tax.

The Executive Mayor of Miami-Dade County is elected countywide to serve a four-year term. The Mayor is not a member of the County Commission. The Mayor appoints a County Manager, with approval and consent of the Board of County Commissioners, to oversee the operations of the County Departments. The Mayor has veto power over the Commission. The post is filled by Carlos A. Giménez.

The Board of County Commissioners is the legislative body, consisting of 13 members elected from single-member districts. Members are elected to serve four-year terms, and elections of members are staggered. The Board chooses a Chairperson, who presides over the Commission, as well as appoints the members of its legislative committees. The Board has a wide array of powers to enact legislation, create departments, and regulate businesses operating within the County. It also has the power to override the Mayor's veto with a two-thirds vote.

Florida's Constitution provides for six elected officials to oversee executive and administrative functions for each county (called "Constitutional Officers"): Sheriff, Property Appraiser, Supervisor of Elections, Tax Collector, Clerk of the Circuit Court and Comptroller. However, the current Constitution allows voters in home-rule counties (including Miami-Dade) to abolish the offices and reorganize them as subordinate County departments; Miami-Dade voters chose this option for Sheriff, Supervisor of Elections, Controller and Tax Collector. The office of Clerk of the Circuit Court, and the judicial offices of State Attorney, and Public Defender, are still branches of State government and are, therefore, independently elected and not part of County government.[citation needed]

The most visible distinction between Miami-Dade and other Florida counties is the title of its law enforcement agency. It is the only county in Florida that does not have an elected sheriff, or an agency titled "Sheriff's Office."[citation needed] Instead, the equivalent agency is known as the Miami-Dade Police Department, and its leader is known as the Metropolitan Sheriff and Director of the Miami-Dade Police Department. However, the badges of Miami-Dade police officers still have "Deputy Sheriff, Dade County, Fla." inscribed.

Miami-Dade Fire Rescue is also the home to Urban Search and Rescue Florida Task Force 1 as well as EMS operations consisting of 57 Advanced Life Support units staffed by 760 state-certified paramedics and 640 state-certified emergency medical technicians.

The Miami-Dade Police Department is a full service metropolitan police department serving Miami-Dade County's unincorporated areas, although they have lenient mutual aid agreements with other municipalities, most often the City of Miami Police Department. The Miami-Dade Police Department is the largest police department in the state of Florida with over 4,700 employees. The Department is still often referred by its former name, the Metro-Dade Police or simply Metro.

The Miami-Dade Police Department operate out of nine districts throughout Miami-Dade County and have two special bureaus. The current director of the department is J. D. Patterson, Jr., who succeeded James Loftus. The Department's headquarters are located in Doral, Florida.

Miami-Dade Water and Sewer Department (MDWASD) is one of the largest public utilities in the United States, employing approximately 2,700 employees as of 2007. It provides service to over 2.4 million customers, operating with an annual budget of almost $400 million. Approximately 330 million gallons of water are drawn everyday from the Biscayne Aquifer for consumer use. MDWASD has over 7,100 miles (11,400 km) of water lines, a service area of 396 square miles (1,026 km2) and 14 pump stations. MDWASD has over 3,600 miles (5,800 km) of sewage pipes, a service area of 341 square miles (883 km2) and 954 pump stations.[59]

Miami International Airport, located in an unincorporated area in the county, serves as the primary international airport of the Miami Area. One of the busiest international airports in the world, Miami International Airport caters to over 35 million passengers a year. Identifiable locally, as well as several worldwide authorities, as MIA or KMIA, the airport is a major hub and the single largest international gateway for American Airlines, the world’s largest passenger air carrier. Miami International is the United States’ third largest international port of entry for foreign air passengers (behind New York's John F. Kennedy International Airport and Los Angeles International Airport), and is the seventh largest such gateway in the world. The airport’s extensive international route network includes non-stop flights to over seventy international cities in North and South America, Europe, Asia, and the Middle East.

In Florida a Tolled State Road is often (but not always) denoted by having the word "TOLL" printed on the top of the State Road shield.

When a driver passes through a toll plaza without paying the proper toll a digital image of the cars license tag is recorded. Under Florida Law, this image can be used by the Authority to issue a toll violation.[62]

Miami-Dade County has 10 major expressways and 1 minor expressway in Downtown Miami.

A street grid stretches from downtown Miami throughout the county. This grid was adopted by the City of Miami following World War I after the United States Post Office threatened to cease mail deliveries in the city because the original system of named streets, with names often changing every few blocks and multiple streets in the city sharing the same name, was too confusing for the mail carriers.[64] The new grid was later extended throughout the county as the population grew west, south, and north of city limits. The grid is laid out with Miami Avenue as the meridian going North-South and Flagler Street the baseline going east-west. The grid is primarily numerical so that, for example, all street addresses north of Flagler and west of Miami Avenue have NW in their address (e.g. NW 27th Avenue). Because its point of origin is in downtown Miami which is close to the coast, the NW and SW quadrants are much larger than the SE and NE quadrants. Many roads, especially major ones, are also named, although, with a few notable exceptions, the number is in more common usage among locals. Although this grid is easy to understand once one is oriented to it, it is not universal in the entire county. Hialeah uses its own grid system which is entirely different in its orientation. Coral Gables and Miami Lakes use named streets almost exclusively, and various smaller municipalities such as Florida City and Homestead use their own grid system along with the Miami-Dade grid system adding to the confusion. In the beach cities and parks of Miami Beach, Surfside, Bal Harbor, Haulover, Sunny Isles, and Golden Beach, the streets are coordinated with the main grid; however, their avenues are named.